Prior Art
The prior art is believed to be best exemplified by the following patents and literature references:
Hochwalt et al U.S. Pat. No. 2,168,160--08/39 PA1 Hochwalt et al U.S. Pat. No. 2,282,518--05/42 PA1 Ball et al U.S. Pat. No. 2,997,466--08/61 PA1 Webster U.S. Pat. No. 3,216,839--11/65 PA1 Herrick et al U.S. Pat. No. 3,454,508--07/69 PA1 Read U.S. Pat. No. 3,551,405--12/70 PA1 Enkvist U.S. Pat. No. 3,864,291--02/75 PA1 Johansson U.S. Pat. No. 4,113,542--09/78 PA1 (1) reacting a mixture of phenol, formaldehyde and water in the presence of sodium hydroxide under reflux conditions for a period sufficient to produce a partially condensed phenol-formaldehyde resin; PA1 (2) forming a mixture of the partially condensed phenol-formaldehyde resin with sodium hydroxide, formaldehyde and a lignin concentrate solution having at least 40% solids comprising normally water-insoluble and phenol-insoluble alkali lignin dissolved in a solvent selected from the group consisting of (a) phenol and water and (b) phenol, water and sodium hydroxide or ammonia; the lignin to phenol weight ratios in said solutions being less then 70:30 and more than 40:60 and said sodium hydroxide or ammonia being present in amounts of 2 to 20% based on the weight of lignin or phenol in the solution; and PA1 (3) reacting said mixture to form a lignin-phenol-formaldehyde resin.
Nam et al, Wood Research, Vol. 40, pp. 1-17 Kyoto, Japan, March, 1967.
Merewether, "The Precipitation of Lignin from Eucalyptus Kraft Black Liquors," TAPPI, Vol. 45, No. 2, pp. 159-163, February, 1962.
Dolenko et al, "Resin Binders From Kraft Lignin," Forest Products Journal, Vol. 28, No. 8, pp. 41-46, August 1978.
Forss et al, "Finnish Plywood, Particleboard, and Fiberboard Made With A Lignin-Base Adhesive," Forest Products Journal, Vol. 29, No. 7, pp. 39-43, July, 1979.
Adams et al, U.S. patent application Ser. No. 097,052 filed Nov. 23, 1979 entitled "High Solids, Low Viscosity Lignin Solutions."